It is known to employ automated systems and processes for monitoring slump and other properties of concrete contained in rotating mixer drums, such as mixer drums that are mounted on concrete delivery trucks. The hydraulic pressure required to rotate the concrete in the mixer drum can be measured by a processor unit on a continuous basis and correlated with the property of the concrete being mixed, and adjustments can be made to the concrete through additions of water or chemical as controlled by the automated system processor unit.
In US 2012/0020180 A1 (owned by the same assignee hereof), Koehler et al. taught that variations in the energy or hydraulic pressure monitored during successive instances during rotation of the mixer drum could be compared by a processor unit with stored variations in the energy or hydraulic pressure as previously derived by the processor unit during successive instances of drum rotation. Thus, it is claimed that segregation and other properties of the concrete can be monitored by examining slight changes in energy or hydraulic pressure expended per drum rotation over time.
Segregation is present when the cement paste matrix no longer holds the aggregate together uniformly within the fluid volume of the mix, and separation of the aggregate from the cement paste occurs. In ASTM C125-11, the term “segregation” is defined as the “unintentional separation of the constituents of concrete or particles of an aggregate, causing a lack of uniformity in their distribution.” Such separation may occur while the concrete is being moved, so-called “dynamic segregation,” and separation may also occur in the quiescent state when the concrete is not being agitated or mixed, and this is otherwise called “static segregation.”
Improper aggregate grading, aggregate shape, and other factors may cause concrete to become segregated, and such factors may arise outside of the knowledge of the concrete manufacturer. Segregation can cause the concrete to be rejected at the job site, or, if such a segregated concrete is poured and placed at the job site, the hardened concrete is likely to result in a weak, porous, and non-durable structure. In serious cases, concrete that has segregated but has been placed will need to be removed and replaced, causing job delays and cost increases. If the materials are known in advance to be susceptible to this problem, the mix designer can exercise greater care in selection and proportioning of ingredients, but day-to-day variations in raw material and mixing behavior can result in undetected segregation occurrences and serious consequences.
It is an objective of the present invention to improve dynamic segregation monitoring by providing specific protocols for detecting and confirming the existence of this condition such that adjustments to the concrete and other actions can be taken.